Update CONTRIBUTING.rst
Update CONTRIBUTING.rst

Numerous changes.
chtyim/cdap,mpouttuclarke/cdap,mpouttuclarke/cdap,caskdata/cdap,chtyim/cdap,hsaputra/cdap,mpouttuclarke/cdap,caskdata/cdap,hsaputra/cdap,chtyim/cdap,caskdata/cdap,chtyim/cdap,mpouttuclarke/cdap,mpouttuclarke/cdap,hsaputra/cdap,hsaputra/cdap,caskdata/cdap,caskdata/cdap,hsaputra/cdap,caskdata/cdap,chtyim/cdap,chtyim/cdap